Let me start out with the observation that the prices of gasoline and diesel are high. Obviously the price of crude has a big effect.
What I want to zero in on is the fact that diesel fuel costs eighty cents a gallon more than regular unleaded (or premium for that matter) gasoline. The US is pretty much alone in that difference.
This table is in euros.
From the link:
91 Octane Gasoline: 1.34
Spread: Gasoline is 10% more expensive than diesel
91 Octane Gasoline: 1.39
Spread: Gasoline is 5% more expensive than diesel
91 Octane Gasoline: 0.97
Spread: Gasoline is 29% more expensive than diesel
91 Octane Gasoline: 0.94
Spread: Gasoline is 26% more expensive than diesel
91 Octane Gasoline: 1.43
Spread: Gasoline is 18% more expensive than diesel
But at my local gas station
91 Octane Gasoline: $3.83
Spread: Diesel is 16% more expensive than premium gasoline
So lets put the myth - that the spread of diesel over gasoline has anything whatsoever to do with world demand - down as being busted. In most countries that tend to prefer diesel cars, diesel is less expensive than gasoline. But in the US the reverse is true.
There is only one plausible reason: Ultra-Low (15 ppm) Sulfur Fuel is required ONLY in the US. It costs more money to remove the sulfur. This relationship was not true at all in 2006, prior to the advent of ULSD requirements. Gasoline and diesel cost roughly the same (gasoline was more expensive in summer, diesel more expensive in winter) prior to ULSD.
Diesel in the US is more expensive than gasoline and you can exclusively thank the EPA.